I should add the IEC 61938 standard from 1996 does reference 120 ohms. And some manufactures (especially with those headphones marketed for professional studio use) design to that standard. But few of the amps everyone favors on these forums have a 120 ohm output impedance. And companies like Sennheiser and Grado claim they design for zero ohms.

The difference can be substantial. Here's a plot I did showing a 50 ohm output impedance with no load in yellow, and what happens with the UE SuperFi 5 IEMs in light blue while the red plot shows the same headphones with a 2 ohm output impedance:

And, many may have seen it before, but Stereophile published similar (if somewhat less dramatic) results with the AKG K530 here:

Art & Science of Measuring Headphones

The Wolfson WM8741 DAC chips have a voltage output of 2Vrms with a full scale digital signal. 2Vrms is about 5.7Vp-p. The DAC chips can only handle a PS of up to 5.5V, and are really recommended to run at 5V (actually, they can take 7V, but Wolfson will tell you never to actually run them over 5.5V). Anyhow, suffice it to say that the chips clip. They have an option to cut the signal by 2dB which results in 4.5Vp-p (~1.59Vrms) which they do just fine with.

Actually, the WM8741's "2Vrms" output amplitude at 0dBFS is differential, so each of the + and - outputs is half that at 1Vrms (2.83Vp-p). The chip will not clip as you stated.